Electromagnetic directional control valve

ABSTRACT

A spool of a valve main body is switched and driven by exciting a solenoid coil by supplying a DC or AC voltage. An intensity of the magnetism generated by the excitation of the solenoid coil is detected by a magnetic sensor. When a predetermined sensor output is obtained, an indicator lamp is lit to indicate that the spool has operated correctly. The intensity of the magnetism due to the DC excitation is detected by magnetoresistive devices. The intensity of magnetism due to the AC excitation is detected by a pickup coil or a current transformer.

This application is a division of application Ser. No. 331,381, filed onMar. 31, 1989, now U.S. Pat. No. 4,953,590.

BACKGROUND OF THE INVENTION

The present invention relates to an electromagnetic directional controlvalve for transferring the motion of an iron core, movable uponexcitation of a solenoid coil, to a spool and for switching betweenfluid passages of a valve main body and, more particularly, to anelectromagnetic directional control valve for detecting whether amagnetic field which drives the movable iron core has been generated bythe application of a DC voltage to the solenoid coil.

FIG. 1 shows a cross sectional view of a conventional electromagneticdirectional control valve.

In FIG. 1, reference numeral 10 denotes a valve main body operable forswitching between fluid passages; 12 indicates an electrical equipmentbox to which a cable for supplying an electric signal from the outsideis connected; and 14 represents a solenoid section.

A spool 16 is assembled into the valve main body 10 so as to be slidablein the axial direction. The spool 16 is held at the neutral positionshown in the diagram by springs 18-1 and 18-2 arranged on both sides ofthe spool 16. The passage in the valve main body 10 can be switched bymoving the spool 16 to the right or left of the neutral position.

The solenoid portion 14 arranged on the left side of the valve main body10 has a casing 20 made of a synthetic resin material. A coil 22 isassembled in the casing 20. The coil 22 is enclosed in a box-shaped coilframe 26 made of a permeable material in a state in which the coil iswound around a coil bobbin 23. A core tube 25 is provided in the coilframe 26. A movable iron core 24 is assembled in the core tube 25 so asto be movable in the axial direction. A fixed iron core 28 is arrangedand fixed on the right side of the movable iron core 24 at apredetermined distance therefrom. A through hole is formed in the fixediron core 28 in the axial direction. A push pin 30-2 is pierced into thethrough hole. The right end of the push pin 30-2 is coupled with thespool 16 and the left end is coupled with the movable iron core 24.

The right end of the core tube 25 is fitted into the hole formed in theedge surface of the valve main body 10 and is fixed by attaching aflange 35 to the valve main body 10 by using a screw 37. On the otherhand, a plug 27 is fitted from the inside of the core tube 25 into thehole formed therein on the left side of the core tube, thereby closingthe left side of the core tube.

A terminal plate 32 is provided in the electrical equipment box 12attached on the valve main body 10. The cable led in from the outside isconnected to a terminal of the terminal plate 32. A DC voltage isapplied to the coil 22 provided in the solenoid section 14 through asignal line from the terminal plate 22, thereby exciting the coil.

An indicator lamp 34 which can be observed from the outside is alsoprovided in the box 12. When a DC voltage is applied from the outside toexcite the coil 22, the indicator lamp 34 is lit to indicate that theelectromagnetic valve has operated.

According to the operation of such a conventional electromagneticdirection control valve, when the coil 22 of the solenoid section 14 isexcited by supplying a DC power source from the outside, the movableiron core 24 is driven to the right by the magnetic field generated fromthe coil 22. The spool 16 is pushed by the push pin 30-2, therebyswitching the passage in the valve main body 10.

At this time, the indicator lamp 34 provided in the electrical equipmentbox 12 is lit to indicate the operation of the electromagneticdirectional control valve. However, even if the indicator lamp 34 islit, it is impossible to check whether the coil 22 had actually beenexcited and the spool 16 actually moved.

To check whether the spool 16 has been moved to the correct position ornot by the excitation of the coil 22 as mentioned above, hitherto, amicroswitch 38 has been provided in a cover 36 on the right side of thevalve main body 10. A push pin 30-1 coupled to the right side of thespool 16 is arranged so as to face a switch knob 40 of the microswitch38. The indicator lamp 34 is lit by the actuation of the microswitch 38.

Therefore, when the movable iron core 24 is moved to the right uponapplication of the DC magnetic field generated by the excitation of thecoil 22 and the spool 16 is moved by the push pin 30-2, the push pin30-1 coupled with the right side of the spool 16 pushes the switch knob40 to thereby actuate the microswitch 38. The indicator lamp 34 is litupon actuation of the microswitch 38, so that it is possible to confirmthat the spool 16 has operated properly.

When the current supply to the coil 22 is stopped, the spool 16 isreturned to the neutral position shown in the diagram by the forces ofthe springs 18-1 and 18-2.

However, the conventional electromagnetic directional control valve,which utilizes a mechanism for checking the operation of the valve bydetecting the motion of the spool 16 by way of microswitch 38, has thefollowing problems.

First, in the electromagnetic directional control valve in which thesolenoid section 14 is attached on one side, for instance, the left sideof the valve main body 10 as shown in the diagram, causes the overallsize of the electromagnetic direction control valve to be larger thanwould otherwise be necessary. This will, in turn, require an enlargedarea for installation of the valve.

Also, since the spool 16 is required to push the switch knob 40 of themicroswitch 38, it is necessary that sufficient force is generated todepress the switch knob 40.

Further, the spacing between the push pin 30-1 and the switch knob 40must be correctly adjusted so that the microswitch 38 is actuated whenthe spool 16 reaches a predetermined position. This spacing adjustmentis complicated.

In addition, since the microswitch 38 is provided on one side of thevalve main body 10, it is impossible to realize a construction in whichthe solenoid sections are attached to both sides of the valve main body10 and, thus, in which the spool is switchable between three positionssuch as those which define straight, neutral and crossed fluid passages.That is, such a construction limits the valve to a two-position valve.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an electromagneticdirectional control valve in which the correct operation of a spool ischecked by detecting a change in the DC magnetic field which isgenerated when a solenoid coil is excited by supplying a DC voltagethereto.

Another object of the invention is to provide an electromagneticdirectional control valve in which the correct operation of a spool ischecked by a magnetic sensor which detects a change in the DC magneticfield.

Still another object of the invention is to provide an electromagneticdirectional control valve in which the correct operation of a spool ischecked by detecting an alternating field which is generated when asolenoid coil is excited by supplying an AC voltage thereto.

Still another object of the invention is to provide an electromagneticdirectional control valve in which the correct operation of a spool ischecked by a pickup coil which detects an alternating current field.

Still another object of the invention is to provide an electromagneticdirectional control valve in which the correct operation of a spool ischecked by a current transformer which detects an alternating currentfield.

That is, in an electromagnetic directional control valve of the type inwhich a DC voltage is supplied, a magnetic sensor using amagnetoresistive device is provided near a coil of a solenoid section,and an output of the magnetic sensor responsive to a DC magnetic fieldof the exciting coil is detected by a detecting circuit, such that it ispossible to check whether the spool of the electromagnetic directionalcontrol valve has operated properly.

Alternatively, in an electromagnetic directional control valve of thetype in which an AC voltage is applied, a pickup coil is provided near acoil of a solenoid section, an output voltage of the pickup coil whichwas induced by an alternating field generated by the excitation of thecoil is detected by a detecting circuit to determine whether thealternating field lies within a predetermined range, such that it ispossible to check whether a spool of the electromagnetic directionalcontrol valve has operated properly.

Similarly, in an electromagnetic directional control valve of the typein which an AC voltage is applied, the operation can be checked byproviding a current transformer to detect an exciting current flowingthrough a coil of a solenoid section.

The above and other objects, features, and advantages of the presentinvention will become more apparent from the following detaileddescription in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a conventional electromagneticdirectional control valve;

FIG. 2 is a cross sectional view showing an embodiment of a DCexcitation type electromagnetic directional control valve according tothe invention;

FIG. 3 is a cross sectional view showing another embodiment of a DCexcitation type electromagnetic directional control valve.

FIG. 4 is a schematic diagram of magnetic sensors and detecting circuitsprovided in the embodiments of FIGS. 2 and 3;

FIG. 5 is a diagram illustrating output characteristics of the magneticsensor in FIG. 4;

FIG. 6 is a cross sectional view showing an embodiment of an ACexcitation type electromagnetic control valve according to theinvention;

FIG. 7 is a schematic diagram of a pickup coil and a detecting circuitin the embodiment of FIG. 6;

FIG. 8 is a diagram illustrating input/output characteristics of thedetecting circuit in FIG. 7;

FIG. 9 is a diagram illustrating detecting characteristics of the pickupcoil in FIG. 7;

FIG. 10 is a cross sectional view showing another embodiment of an ACexcitation type electromagnetic control valve;

FIG. 11 is a schematic diagram of a current transformer (i.e. currentdetecting transformer) and a detecting circuit utilized in theembodiment of FIG. 10;

FIG. 12 is a diagram illustrating detecting characteristics of thecurrent transformer in FIG. 11; and

FIG. 13 is a diagram illustrating input/output characteristics of thecurrent transformer in FIG. 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 is a cross sectional view showing an embodiment of the presentinvention as applied to a DC excitation type electromagnetic directionalcontrol valve.

In FIG. 2, the spool 16 is slidably assembled in the valve main body 10.The spool 16 is supported at the neutral position shown in the diagramby the springs 18-1 and 18-2 arranged on both sides of the spool 16. Bysupplying a current to the solenoid coil, the spool 16 is moved to theright or left of the neutral position, thereby switching the internalfluid passage.

The electrical equipment box 12 is attached onto the valve main body 10.In the box 12 are disposed a terminal plate 32 to which is connected acable which is led in from the outside and an indicator lamp 34 which islit when the spool is moved to the right or left position. Also providedis a plug 42 which is used to provide electrical connection withsolenoid sections 14-1 and 14-2.

The solenoid sections 14-1 and 14-2 are attached to both sides of thevalve main body 10. An internal structure of the solenoid section 14-1on the right side is shown as a cross sectional view.

The solenoid section 14-1 has the casing 20 made of a synthetic resinmaterial. The cylindrical coil 22 supported within the box-shaped coilframe 26 made of a permeable material is disposed within the hollowportion in the casing 20 and is wound around the coil bobbin 23. Thecore tube 25 is inserted into the coil 22. The movable iron core 24which is slidable in the axial direction is arranged in the core tube25. The fixed iron core 28 is spaced from the left side of the movableiron core 24 by a predetermined distance L. The fixed iron core 28 isfixed to the valve main body 10 by securing the core tube 25 to thevalve main body 10 by way of flange 35 and screw 37. A through hole isformed at the center of the fixed iron core 28 in the axial direction.The push pin 30-1 whose one end is coupled with the spool 16 is movablyinserted into the through hole. The left side of the push pin 30-1 iscoupled with the movable iron core 24.

The coil 22 is connected to a terminal of the terminal plate 32 by asignal line which is connected to the plug 42 by a receptacle 44.

Although the structure of such an electromagnetic directional controlvalve is substantially the same as that of the conventional valve, itdiffers from the conventional valve in that it additionally includes amagnetic sensor 46 attached in the casing 20 near the right side of thecoil frame 26 in the solenoid section 14-1. Furthermore, a detectingcircuit 48 is installed in the box 12. The detecting circuit 48 isconnected by a signal line to the magnetic sensor 46 of solenoid section14-1 by way of the plug 42 and receptacle 44. A DC magnetic fieldgenerated by the coil 22 is detected by the magnetic sensor 46 so as tocause lighting of the indicator lamp 34 and transmittal of a detectionsignal to the outside as necessary. The solenoid section 14-2 isdisposed on the side of the valve opposite solenoid section 14-1 and hassubstantially the same structure as the solenoid section 14-1.

The operation of the embodiment shown in FIG. 2 will now be described.

When a DC voltage is supplied from the outside, a DC current flowsthrough the coil 22 which has a hollow cylindrical shape so as togenerate a DC magnetic field and form a magnetic circuit through thecoil frame 26, fixed iron core 28, and movable iron core 24. Therefore,a magnetic attractive force is generated between the fixed iron core 28and the movable iron core 24 such that the movable iron core 24 is movedto the left against the forces of the springs 18-1 and 18-2. At the sametime, the spool 16 is moved to the left by the push pin 30-1 and thepassage in the valve main body 10 is switched. When the spool 16 movesto the switching position and stops, the resistance of the magneticcircuit in which the coil 22 is used as a magnetism generating source isminimized, while the magnetic field becomes maximum.

When the current supply to the coil 22 is stopped, the generation of themagnetic field is stopped and the movable iron core 24 and spool 16 arereturned to the neutral position, shown in the diagram, by the forces ofthe springs 18-1 and 18-2.

When the coil 22 is excited by applying a DC voltage thereto, themagnetic flux which is generated through the coil frame 26 causes themagnetic sensor 46 arranged near the coil frame 26 to output an electricsignal corresponding to the direction and magnitude of the DC magneticfield. An output of the magnetic sensor 46 is transmitted through thereceptacle 44 and plug 42 and is input to the detecting circuit 48provided in the box 12.

The detecting circuit 48 outputs an H level signal which is set to thelogic level "1" when the output of the magnetic sensor 46 exceeds apredetermined threshold value V_(ref), thereby lighting the indicatorlamp 34 as an indication of the operation of the valve.

Alternatively, by transmitting the H level output signal of thedetecting circuit 48 to the outside from the box 12 and affecting adisplay, the operation of the electromagnetic directional control valvecan be confirmed from a remote position.

FIG. 3 is a cross sectional view showing another embodiment of a DCexcitation type electromagnetic directional control valve. Theembodiment is characterized in that the detecting circuit 48 is arrangednear the magnetic sensor 46 provided in the casing 20 of the solenoidsection 14-1. In the embodiment of FIG. 3, the detecting circuit 48 isarranged near the magnetic sensor 46 so that the signal line leadingfrom the sensor is short in length and erroneous detection signals dueto noises are prevented.

FIG. 4 shows a schematic illustration of the magnetic sensor 46 anddetecting circuit 48 shown in each of FIGS. 2 and 3.

In FIG. 4, the magnetic sensor 46 is formed of a pair ofmagnetoresistive devices 52 and 54 made of thin films of a magneticmaterial whose resistance values change due to the influence of themagnetic field incident on a board 50. The magnetoresistive devices 52and 54 are arranged so as to cross perpendicularly in a manner in whichone end of each of the devices is commonly used. A predetermined voltageof a DC power source 56 provided for the detecting circuit 48 is appliedto both ends of the devices 52 and 54.

Practically speaking, the magnetoresistive devices 52 and 54 are formedby thin films made of a ferromagnetic metal such as Fe-Ni or Co-Ni.

When the magnetoresistive devices 52 and 54 are assembled in the casing20 as shown in FIGS. 2 and 3, a magnetic field is applied to the devices52 and 54 from a direction shown by an arrow 58 (FIG. 4). The resistancevalues of the devices 52 and 54 change in accordance with the directionand intensity of the magnetic field. Therefore, a divided voltage, basedon the resistance values of the two magnetoresistive devices 52 and 54and proportional to the DC magnetic field which changes depending on themotion of the movable iron core 24, is derived from the magnetic sensor46.

In this case, since the output of the magnetic sensor 46 is adifferential output, the fluctuation components of the resistance valuesdue to a change in ambient temperature are offset and a stable outputwhich is not influenced by the ambient temperature is obtained.

The output of the magnetic sensor 46 is input to a comparator 55 in thedetecting circuit 48 and is compared with the threshold voltage V_(ref)which is set by the reference voltage source 56.

That is, an output voltage is obtained by dividing a predeterminedvoltage from the DC power source 56 by the resistance values of themagnetoresistive devices 52 and 54 which make up the magnetic sensor 46.By setting the threshold value V_(ref) to a value which is significantlysmaller than the output of the magnetic sensor 46 when the movable ironcore 24 is located at a predetermined operating position, for instance,at the position where the movable iron core 24 is in contact with thefixed iron core 28, it is possible to detect, by a comparison outputfrom the comparator 55 in the detecting circuit 48, whether or not themovable iron core has moved into contact with the fixed iron core 28.That is, whether or not the spool 16 of the electromagnetic directionalcontrol valve has moved to the correct position can be detected.

FIG. 5 shows an example of an operating characteristic of the magneticsensor 46. That is, as shown in FIGS. 2 and 3, a spacing L is providedbetween the movable iron core 24 and the fixed iron core 28 in theinoperative mode in which the spool is located at the neutral position.The graph in FIG. 5 shows the change which occurs in the output voltageV_(out) of the magnetic sensor 46 when the movable iron core 24 movesdue to the DC excitation of the coil 22 and the interval L changes from6 mm to 0 mm.

As will be obvious from FIG. 5, when the movable iron core 24 approachesthe position at which the movable iron core 24 comes into contact withthe fixed iron core 28 (L=0 mm), the output V_(out) of the magneticsensor 46 suddenly increases due to the increase in intensity of themagnetic field passing through the magnetic sensor 46. Therefore, bysetting the threshold value V_(ref) for the detecting circuit 48 to alevel shown in the graph which is lower than the sensor output when L=0mm, operation of the movable iron core 24 to move the spool 16 to thecorrect position can be detected.

An attractive force F between the fixed iron core 28 and the movableiron core 24 in the solenoid section 14-1 is obtained by the followingequation.

    F=K·(N·I/x).sup.2 ·S

where,

K: constant,

N: the number of turns of the coil,

x: stroke of the movable iron core,

I: coil exciting current,

S: area of the absorbing section.

Therefore, the stroke position of the movable iron core 24 correspondsto the output of the magnetic sensor 46. By monitoring the sensoroutput, the operation of the electromagnetic directional control valvecan be correctly detected.

FIG. 6 is a cross sectional view showing an embodiment of the presentinvention which is applied to an AC excitation type electromagneticdirectional control valve.

In FIG. 6, as shown in the solenoid section 14-1 on the left side of thevalve main body 10, the coil 22 wound around a coil bobbin is assembledinto the casing 20 made of a synthetic resin material. The coil 22 issupported by coil frames 260 and 262 made of a permeable material. Thecoil frames 260 and 262 are formed of silicon steel plates. A pickupcoil 62 is arranged near the coil frame 260. The pickup coil 62 has astructure in which a coil is wound a predetermined number of timesaround an iron core having a high permeability. When an alternatingfield is applied to the pickup coil 62 by the AC excitation of the coil22, it generates an inductive voltage.

A detecting circuit 64 is provided in the electrical equipment box 12arranged on the valve main body 10. A signal line which is led out fromthe pickup coil 62 provided in the solenoid section 14-1 is connected tothe detecting circuit 64 through the receptacle 44 and plug 42. When anoutput voltage of the pickup coil 62 is within a predetermined thresholdrange, the detecting circuit 64 generates a detection output signal andlighting of the indicator lamp 34 and, if necessary, sends a detectionsignal to the outside.

The remainder of the structure shown in FIG. 6 is substantially the sameas that shown in the embodiment of FIGS. 1 and 2 except that in theembodiment of FIG. 6 the fixed iron core 28 and movable iron core 24 inthe solenoid section 14-2 are assembled into the casing 20 by adifferent core tube 264, a screw plug 96, and plugs 94 and 27.

FIG. 7 schematically illustrates the pickup coil 62 and detectingcircuit 64 of the embodiment shown in FIG. 6.

In FIG. 7, the pickup coil 62 is constructed by winding a coil 68 arounda rod-shaped iron core 66 having a high permeability. When analternating field H is applied by the AC excitation of coil 22 (FIG. 6)to the pickup coil 62 from a direction indicated by an arrow 65, thepickup coil 62 induces an AC voltage in the coil 68.

The detecting circuit 64 has a first comparator 70 and a secondcomparator 74. An output voltage E₀ of the pickup coil 62 is applied toa negative input terminal of the first comparator 70 through a resistorR₁ and is also applied to a positive input terminal of the secondcomparator 74 through a resistor R₃. A first threshold voltage E₁ isapplied from a reference voltage source 72 to a positive input terminalof the comparator 70 through a resistor R₂ and a second thresholdvoltage E₂ is applied from a reference voltage source 76 to a negativeinput terminal of the comparator 74 through a resistor R₄. The thresholdvoltages E₁ and E₂ are set so that E₁ <E₂. When the output voltage E₀ ofthe pickup coil 62 is within a range between the threshold voltage E₁and the threshold voltage E₂, both of the comparators 70 and 74 generateH level outputs. That is, the comparators 70 and 74 define a windowcomparator.

The output of the comparators 70 and 74 are input to an AND gate 78. Anoutput of the AND gate 78 is input to a delay circuit 80. An output ofthe delay circuit 80 becomes a final detection output of the detectingcircuit 64.

The operation of the embodiment of FIG. 6 will now be described.

When an AC voltage is applied from the outside to the coil of thesolenoid section 14-1, an AC exciting current flows through the coil 22,so that an alternating field is generated. A magnetic flux H of thealternating field generated by the excitation of the coil 22 interlinksthe pickup coil 62 as shown in FIG. 7. The voltage induced in the coil68 is input to the detecting circuit 64.

FIG. 8 shows input/output characteristics of the comparators 70 and 74provided in the detecting circuit 64. An axis of abscissa denotes aninput as an output voltage E₀ of the pickup coil 62 and an axis ofordinate indicates an output which is set to a logic level H or L.

As will be obvious from FIG. 8, since there is the relation of E₁ <E₂between the threshold voltages E₁ and E₂ for the comparators 70 and 74,the logic outputs of the comparators 70 and 74 are set as follows forthe inductive voltage E₀ of the pickup coil 62.

    ______________________________________                                                   Comparator 70                                                                           Comparator 74                                            ______________________________________                                        E.sub.0 < E.sub.1                                                                          L           H                                                    E.sub.1 < E.sub.0 < E.sub.2                                                                H           H                                                    E.sub.2 < E.sub.0                                                                          H           L                                                    ______________________________________                                    

Therefore, when the inductive voltage E₀ of the pickup coil 62 lieswithin the range between the threshold values E₁ and E₂, the outputs ofthe comparators 70 and 74 are set to the H level and an H level outputis derived from the AND gate 78. The H level output signal is delayed bythe delay circuit 80 by a time corresponding to the response time fromthe start of the excitation of the coil 22 to the completion of theswitching of the spool 16. Thereafter, the H level output is obtainedfrom the detecting circuit 64. The indicator lamp 34 is caused to lightby the H level output, thereby indicating that the electromagneticdirectional control valve has operated.

FIG. 9 shows a time-dependent change of the inductive voltage of thepickup coil 62 upon application of the AC voltage to the coil 22 formoving the movable iron core 24.

As shown in FIG. 6, the pickup coil 62 is arranged near the coil frame260 formed of silicon steel plates having a high permeability. Themovable iron core 24 is attracted to the fixed iron core 28 upon theformation of the magnetic circuit due to the alternating field generatedby the AC excitation of the coil 22. At the same time, the spool 16 isalso pushed by the movable iron core 24 through the push pin 30-1 and ismoved left from the neutral position shown in the diagram to the leftswitching position.

The density of the magnetic flux which passes through the pickup coil 62becomes maximum soon after initial movement of the movable iron core 24due to the AC excitation of the coil 22 at time t₀ in FIG. 9. Theinductive voltage E₀ of the pickup coil 62 correspondingly rises to thepeak level. As the movable iron core 24 approaches the fixed iron core28, the density of the magnetic flux passing through the pickup coil 62decreases. When the movable iron core 24 comes into contact with thefixed iron core 28 at time t₁ and the spool 16 stops at the switchingposition, the magnetic flux density is held at a predetermined value.Therefore, the inductive voltage of the pickup coil 62 becomes almoststable at a predetermined level after time t₁.

Therefore, by setting the threshold voltages E₁ and E₂, which are setfor the comparators 70 and 74 in the detecting circuit 64 in FIG. 7, tovalues which are higher and lower, respectively, than the predeterminedlevel of the stable voltages of the pickup coil 62 after time t₁ in FIG.9, the movement of the movable iron core 15 upon the AC excitation ofthe coil 22, and the motion of the spool 16, can be correctly detected.

On the other hand, when the coil 22 is excited and the movable iron core24 does not move due to sticking or the like of the spool 16, theinductive voltage E₀ of the pickup coil 62 is stabilized at a voltageoutside the range between the threshold voltages E₁ and E₂ and nodetection output is derived from the detecting circuit 64.

The inductive voltage E₀ of the pickup coil 62 is given by the followingequation.

    E.sub.0 =K·f·N·S·B.sub.m

where,

K: constant,

f: AC frequency,

S: effective cross sectional area of the core,

B_(m) : maximum magnetic flux density,

N: the number of turns of the coil.

Since the inductive voltage E₀ of the pickup coil 62 depends on theintensity of the magnetic flux, a signal is obtained which correspondsto the level of the magnetic flux which interlinks upon operation of themovable iron core 24.

The attractive force F is given by the following equation.

    F=K.sub.0 ·B.sub.M.sup.2 ·S (1-cos2ωt)

where,

K₀ : constant,

ω: angular frequency,

Although the coil 22 pulsates at the frequency which is twice as high asthe frequency of the AC power source and generates noises, pulsation ofthe attracting force can be reduced by providing a shading coil or thelike.

Although only one pickup coil 62 has been provided in the embodiment ofFIG. 6, a change in magnetic flux can be detected at a highersensitivity by using a plurality of pickup coils arranged near the coilframe 260. In such an arrangement, output voltages of the pickup coilsare added and the resultant voltage is input to the detecting circuit64.

FIG. 10 is a cross sectional view showing another embodiment of an ACexcitation type electromagnetic directional control valve according tothe invention. The embodiment is characterized in that current flowingthrough the coil 22 provided in the solenoid section 14-1 is detected bya current transformer.

In FIG. 10, an AC voltage is supplied from the terminal plate 32provided in the electrical equipment box 12 to the coil 22 in thesolenoid section 14-1 by connecting a lead wire 84 from the terminalplate 33 to the plug 42 and by, further, connecting a signal line fromthe receptacle 44 to the coil 22.

A current transformer 86 is attached to the lead wire 84 to connect theterminal plate 32 to the plug 42. As will be clearly describedhereinafter, the current transformer 86 has a structure such that aprimary conductor through which an exciting current flows is piercedinto a ring-shaped iron core having a high permeability. A secondarycoil is wound around the ring-shaped iron core. A voltage proportionalto the AC exciting current flowing through the primary conductor isinduced in the secondary coil.

An output of the current transformer 86 is input to a detecting circuit88 (FIG. 11) and the operation of the electromagnetic directionalcontrol valve is detected.

The remainder of the structure of the electromagnetic valve issubstantially the same as that in the embodiment of FIG. 6.

FIG. 11 schematically illustrates the current transformer 86 anddetecting circuit 88 of the embodiment shown in FIG. 10.

In FIG. 11, the current transformer 86 is constructed in a manner suchthat the lead wire 84 to the coil 22 is used as a primary conductor, theprimary conductor 84 is pierced into a ring-shaped iron core 90 having ahigh permeability, and a secondary coil 92 is wound around the iron core90.

The comparator 88 has the same circuit construction as the comparator 74in FIG. 7. The threshold voltages E₁ and E₂ which are input into thecomparators 70 and 74 by the reference voltage sources 72 and 76 havevalues which are peculiar to the current transformer 86.

FIG. 12 shows a time-dependent change in output voltage E₁₀ of thecurrent transformer 86 upon application of AC power to the coil 22.

When an AC voltage is applied to excite the coil 22 at time t₀ in FIG.12, the movable iron core 24 is attracted toward the fixed iron core 28and the inductive voltage E₁₀ is generated in the current transformer86. That is, the magnetic field according to Ampere's cork screw rule isgenerated around the primary conductor 84 by the exciting currentflowing through the primary conductor 84. The voltage E₁₀ is induced inthe secondary coil 92 of the iron core 90 in accordance with thechanging excitation current. The spool 16 is caused to movesimultaneously with the movement of the movable iron core 24. Theexcitation current to the coil 22 also changes in accordance with themagnetoresistance of the magnetic circuit due to the movement of themovable iron core 24. That is, there is shown a transient response suchthat the inductive voltage E₁₀ of the secondary coil 92 of the currenttransformer 86 rises to the peak level after time t₀ and, thereafter, itdecreases. When the movable iron core 24 comes into contact with thefixed iron core 28 at time t₁ and the spool 16 stops, the inductivevoltage of the secondary coil 92 is stabilized at a predetermined value.

Therefore, by setting the threshold voltages E₁ and E₂ for thecomparators 70 and 74 in FIG. 11 to values which are higher and lower,respectively than the predetermined voltage after time t₁ in FIG. 11, itis possible to detect whether or not the electromagnetic directionalcontrol valve has correctly operated on the basis of the excitingcurrent of the coil 22.

The ratio between the maximum current and the stationary current of theexciting current flowing through the coil 22 is generally about 5:1.

FIG. 13 shows the relation between an ampere-turn (AT) due to thecurrent supply to the primary conductor 84 of the current transformer 86and the inductive voltage E₁₀ of the secondary coil 92. Since a value of5 or more is obtained as a dynamic range of the current transformer 86,the operation of the electromagnetic directional control valve can becorrectly detected by detecting the exciting current or the coil 22.

On the other hand, when the excitation current flows through the coil 22but the movable iron core 24 does not correctly operate due to stickingof the spool or the like, the magnetoresistance value is different froma prescribed value and the value of the exciting current flowing throughthe primary conductor 84 also differs from a prescribed value.Therefore, the inductive voltage E₁₀ of the current transformer 86 whichlies within the range between the threshold voltages E₁ and E₂ is notobtained and no detection output is derived from the detecting circuit88. Thus, the abnormality of the operation is detected.

What is claimed is:
 1. An electromagnetic directional control valvewhich is switched and operated by applying an AC voltage, comprising:avalve main body, which has a spool that is movable in an axial directionfrom a neutral position to at least one other predetermined position,for switching an internal passage; electromagnetic driving means, havingat least one movable core attached to one side of the spool provided insaid valve main body and at least one coil in surrounding relation tosaid at least one movable core, for switching and moving the spool inthe valve main body to a predetermined position by an AC electromagneticforce generated by an AC excitation of said at least one coil; magnetismdetecting means for detecting an intensity of an alternating field whichchanges in accordance with the movement of said at least one movablecore and for producing a detected magnetism output; detecting circuitmeans for generating a detection output when said detected magnetismoutput of said magnetism detecting means lies within a predeterminedrange; and display means for displaying that the valve main body hascorrectly operated on the basis of the detected magnetism output of saiddetecting circuit means.
 2. A valve according to claim 1, wherein saidmagnetism detecting means comprises a pickup coil formed by a coil woundaround a rod-shaped iron core having a high permeability through whichthe alternating field generated by the AC excitation of said at leastone coil passes.
 3. A valve according to claim 1, wherein said magnetismdetecting means comprises a current transformer which includes a primaryconductor extending through a ring-shaped iron core having a highpermeability, and a secondary coil wound around said iron core, saidprimary conductor being defined by a lead wire adapted to supply an ACexciting current to said at least one coil.
 4. A valve according toclaim 1, wherein said detecting circuit means comprises:a firstcomparator which generates an L level output when a detection voltage ofsaid magnetism detecting means is smaller than a first threshold voltageand which generates an H level output when said detection voltage isequal to or larger than said first threshold voltage; a secondcomparator which generates an H level output when the detection voltageof the magnetism detecting means is equal to or smaller than a secondthreshold voltage higher than said first threshold voltage and whichgenerates an L level output when said detection voltage is larger thansaid second threshold voltage; an AND gate for obtaining an AND of theoutputs of said first and second comparators; and a delay circuit todelay an output of said AND gate by a time corresponding to an operatingtime from the current supply to said at least one coil to the completionof the switching of said spool to said predetermined position.